Hospital bed designs have recently been undergoing a transformation. Early beds were very basic devices providing limited patient support and care features. More recently, bed designs have been taking advantage of technological developments to provide improvements in bed articulation, mattress inflation, patient access, convenience and control. The following patents illustrate some of the designs that are currently known.
1. Pneumatic System
Valves are an integral part of a mattress inflation system. Recently, valves have been designed in which a metal alloy that changes shape in response to a change in temperature is used as the valve actuator. In U.S. Pat. No. 3,540,479 issued to Thompson for a "Heat Motor and Valve", a valve using a heat-expanding rod to open a biased-closed valve seat is disclosed. Willson et al., in U.S. Pat. No. 3,613,732 entitled "Temperature-Responsive Valve Operators", discloses various valve configurations utilizing temperature-responsive operators made with a shape-memory alloy such as a nickel and titanium alloy. The disclosed configurations include single and double poppet designs, as well as coaxial, single poppet designs.
U.S. Pat. No. 4,130,265 issued to Sakakibara et al. for "Electrically Operated Switching Valve" discloses the use of a warped plate controlled by a heat-activated element for selectively valving opposing ports relative to an intermediate port. Suzuki, in U.S. Pat. No. 4,736,587 entitled "Shape-Memory Electromechanical Drive" discloses the use of two shape-memory springs to move a slide member to couple alternate outer ports with a central port.
A valve member that alternately opens and closes by heat-generating electrical current acting on a spring-biased linear alloy element is disclosed in U.S. Pat. No. 4,973,024 issued to Homma for "Valve Driven By Shape Memory Alloy". Hori, in Japanese Pat. No. JP61-17789 entitled "Valve Device", discloses a valve-opening device activated by a shape-memory alloy spring. The valve is held closed by a coaxial bias spring.
These valve assemblies provide for effective valving, but there remains a need for a valve assembly that is able to inversely vary the flow of air or other fluid through respective inlet and outlet ports, and to independently control the flow of air through input and output ports, and that is self-contained for convenient installation and removal from a fluid-chamber housing.
Inflatable mattress cushions or cells are often connected to a support surface of a base platform or frame. This connection may be provided by a connector having an inner channel or passageway, that attaches the cell to a port extending through the support surface. Further, it is known to connect two cells together with a passageway formed in the connection to allow air to flow between the connected cells. An example of such an arrangement is disclosed by Pertchik in U.S. Pat. No. 4,255,824 for "Cushion for Decubitus Ulcers". Pertchik discloses a seat cushion formed of a plurality of elongate cells that are connected at contact points to provide inflation of all the cells from a single inlet.
Hunt et al., in U.S. Pat. No. 4,525,885 entitled "Support Appliance for Mounting on a Standard Hospital Bed", discloses male and female parts of a connector assembly for connecting mattress cells to a mattress base inlet or outlet. Another form of connector for a mattress cell is shown in FIG. 6 of U.S. Pat. No. 4,949,413 issued to Goodwin for "Low Air Loss Bed".
Hunt et al., in U.S. Pat. No. 4,935,968 entitled "Patient Support Appliances" also discloses a connector of an air tube to a housing (FIG. 4). This is a quick release connection to allow rapid deflation for cardiac arrest procedures. In U.S. Pat. No. 4,949,414 entitled "Modular Low Air Loss Patient Support System and Methods for Automatic Patient Turning and Pressure Point Relief", Thomas et al. also disclose in FIGS. 5 and 6 a connector for connecting a mattress cell to the platform.
These connectors are constructed to be usable in a specific application, but do not permit use in various connections. For instance, there remains the need for fluid-transmitting connectors that are usable for coupling a cell to a support platform and for coupling cells together, with the integrity of the base cell remaining when a satellite cell is disconnected. Further, there is a need for a connector that can accommodate a reducer for connecting a tube to a cell.
When used on an articulating bed, the fluid supply and exhaust systems used for inflating and deflating mattress cells must either be formed integrally as part of the bed platform, or must be provided by external hoses or ducts. These arrangements result in bending and wear of connecting hoses, and exposure of external tubes to wear and contact by other moving parts.
The present invention makes use of expandable passageways, similar to bellows, for coupling manifolds supported on adjoining, articulating panels. Bellows-like support cells are known to be used in hospital beds. For instance, Hunt et al., in U.S. Pat. No. 4,099,276 entitled "Support Appliances Having Articulated Sections" shows the use of inflatable bellows to raise and lower the head end of a bed platform. Similar structures are also shown in patent '885 issued to Hunt et al., identified previously. A bellows-type mattress cell is disclosed by Sato in U.S. Pat. No. 4,542,547 entitled "Pneumatic Mat with Sensing Means".
There thus remains the need for a flexible passageway structure that can connect air passageways of adjoining bed panels, that conforms with the panel structure, is reliable, and expands and contracts in response to movement of the adjoining panels.
There also is a need for a simple efficient structure for conveying pressurized and exhaust fluids to mattress cells, and along articulated panels. As was mentioned, flexible tubes are usually used to connect mattress cells to an air supply and exhaust port. For example, Hunt et al., in patent '885, and Goodwin, in patent '413, disclose the use of a flexible tube serving each mattress section. Goodwin shows them as being external to the bed platform, while Hunt et al. show them to be within the platform. Also, Evans, in U.S. Pat. No. 4,864,671 entitled "Controllably Inflatable Cushion", discloses individual cushions inflated in groups or zones with supply lines and exhaust lines serving each zone being controlled by a three way valve.
U.S. Pat. No. 4,945,590 issued to Ogura for "Valve for Fluid Mat and Apparatus for Controlling an Attitude Assumed by Fluid Mat", discloses air mattress supply ducts that are positioned between relative positive and negative pressure air chambers. Separate solenoid valves connect each air supply duct with each of the air chambers.
Harkleroad et al. discloses, in U.S. Pat. No. 4,993,920 entitled "Air Mattress Pumping and Venting System", a pressure control system in which sensors control a venting valve and a pump for maintaining the mattress pressure between predetermined high and low values. The use of a valve having a rotatable disk for alternately connecting air supply and discharge pipes to two mattress sections is shown in U.S. Pat. No. 5,035,016 issued to Mori et al. for an "Air-Mat Apparatus".
With the development of elaborate inflatable mattresses and articulating support platforms, it became difficult to take immediate action when a patient needed CPR or other procedures to treat a life-threatening condition. Various means have been developed to make the bed become a hard, flat surface to facilitate, rather than impair these procedures.
For instance, in British Patent No. GB 2 141 333 entitled "Low Air Loss Support Appliance", Hunt et al. disclose in FIG. 2 and on page 2, lines 67-74, a quick release manifold that allows deflation from all ports.
In patent '968, Hunt et al. disclose an air distribution chamber for supplying air to mattress cells. An exhaust plate on the chamber is manually moved to open an exhaust hole for rapidly deflating the mattress. An air pump must be separately turned off, but a switch activated by the handle to the exhaust plate transmits a signal to open the exhaust valves used on the head & foot articulating bellows. FIG. 12 of patent '414 issued to Thomas et al. discloses the use of a CPR switch connected to a circuit board.
Various forms of cushions and mattresses have been designed in order to provide improved support for a patient. Viesturs et al., in U.S. Pat. No. 4,534,078 entitled "Body Supporting Mattress", disclose an elongate inner cell supported on a pad having a peripheral inflated tube. Generally U-shaped cells that alternate and are offset for use in turning a patient are disclosed in U.S. Pat. No. 5,003,654 issued to Vrzalik for a "Method and Apparatus for Alternating Pressure of a Low Air Loss Patient Support System". In U.S. Pat. No. 4,768,249 entitled "Patient Support Structure", Goodwin discloses a more conventional low air loss mattress formed of upright cells extending across the width of the bed.
Such mattresses as shown by Goodwin and Vrzalik are prone to bend or lean into an adjoining cell location when the adjoining cell is deflated. This tends to reduce the effectiveness of controlling the support pressure and location, which is necessary in the avoidance and treatment of bed sores, and also in the articulation of the bed.
It is also known to provide mattresses that have multiple layers. Grant, in U.S. Pat. No. 3,674,019 entitled "Dual Layer Cellular Inflatable Pad", describes a pad formed of offset layers of interdigitated inflatable sections. Welch, in U.S. Pat. No. 4,193,149 entitled "Beds and Mattresses", discloses a similar mattress, except the layer cells are aligned and separated by a preformed foam. Such mattresses assure resilient support for a patient, but provide limited control of support by adjacent cells.
Various cushions are also known for restraining a person. An elaborate example is disclosed by Boyce in U.S. Pat. No. 3,218,103 entitled "Pneumatic Restraint System". This patent discloses a chair having inflatable bands shiftable in position for selectively restraining a person. A restraining device that is releasably attached to a support platform for placement across the body of an infant is disclosed in U.S. Pat. No. 4,205,669 issued to Hamann for "Diaper-Changing Aid".
There thus remains a need for a means for restraining persons on a bed. In particular, it is desirable to have lateral cushions that conform to the sides of a patient, and selectively inflatable cushions that are positionable over a patient for keeping the patient in the bed.
The pneumatic system of a conventional hospital bed typically includes a single pressurized air source with valves and ducts or other conduits providing distribution to the cushions in a mattress. Examples of such systems are provided in U.S. Pat. Nos. 4,799,276, 4,949,413, 4,993,920 and 5,044,029. A review of these patents shows the extent that people have gone in controlling air flow from a single source. The air flow is divided and distributed to cushions supported on several relatively articulatable panels. There typically are elaborate valves to control the amount of air flow and extensive flexible conduits and/or plenums to distribute the allocated air to each set of cushions. The air distribution system described herein with reference to FIG. 2 is an example of a more simplified air distribution scheme, but even it imposes significant structural requirements on the bed panels to form the air flow paths.
The manner in which the cushions are attached to or supported on the platform panels may also be involved. For instance U.S. Pat. Nos. 3,879,776 and 3,909,858 illustrate elaborate structures for attaching inflatable cushions to a bed platform for anchoring the cushions and providing an air passageway for inflating them.
There thus is a need for a pneumatic system that is simple in structure, readily serviced, and provides pressure control to individual sets of cushions supported on relatively articulatable panels.
2. Footboard Gate
In most any patient care environment in which the patient is bedridden, it is desirable, and often necessary to provide support for equipment, documents, and other materials. Where it is sufficient to use a shelf or horizontal platform for this a movable tray on a stand separate from the bed is often utilized. In order to limit the amount of accessories around the bed or to provide a convenient table in the vicinity of the bed, various schemes have been developed.
Slivoski, in U.S. Pat. No. 3,327,328 entitled "Mattress Extension", discloses a bed having a foot-end kick board that swings upward to form a platform. In U.S. Pat. No. 3,344,445 entitled "Side Panel Construction for Stretcher-Beds", Crawford discloses a side guard panel that converts into a platform.
A board extending across an intermediate portion of a bed is disclosed by Donald in U.S. Pat. No. 535,945 entitled "Detachable Foot Rest and Table for Beds". The board is positionable as a table, and may be pivoted down to act as footboard for a person sitting in bed or extended beyond the foot of the bed for storage. A somewhat similar concept is disclosed in U.S. Pat. No. 4,724,555 issued to Poehner et al. for a "Hospital Bed Footboard". This footboard pulls out and pivots up to form a horizontal table. An alternative embodiment simply swings up to a horizontal, over-floor position and can slide partially over the foot of the bed.
3. Stand-Up Board
The extended articulation capabilities of some beds includes the ability to raise the head of the bed, and correspondingly lower the foot of the bed until the bed is sufficiently inclined to allow the patient to exit the bed from a standing position. In order to accommodate this, it is necessary for the bed to have a footboard that is strong enough to hold the weight of the patient, and yet small enough that it will allow the mattress to be lowered near the floor.
A bed developed by England and described in U.S. Pat. No. 3,997,926 entitled "Bed with Automatic Tilting Occupant Support", is positionable in a stand-up position. A foot rest is shiftable between an inoperative position spaced from the end of the bed to an operative position adjacent to the end of the bed when the bed is inclined. The foot rest is disposed at an obtuse angled relative to the platform.
This footboard has limited capabilities, and is always a part of the bed platform. Considering the infrequency that beds are used to raise a patient to a standing position, it is desirable to have a footboard that is adjustable, can serve different functions, and can be removed if desired.
4. Headboard
When CPR or other emergency procedures are performed on a patient the attending personnel desire to be as close as possible to the patient. Surgical tables, for instance, are built without any form of side barriers. Beds, however, are normally used to support a patient when such procedures are not being performed, and therefore have restraining elements, such as side rails, headboards and footboards. It is conventional to provide a side rail that collapses below the level of the mattress to facilitate care by a nurse, doctor or other attendant. The number of attendants that can reasonably access a patient is limited to the number that can conveniently stand along the sides of a bed. There is thus a need for providing increased access to a patient supported in a bed.
Also, for some forms of equipment, tables or trays are not adequate. For instance, intravenous (IV) equipment typically must be suspended above a patient to allow gravity to convey a fluid from a container to an intravenous needle. Also, traction devices must have an anchor connected to the bed frame. These requirements have led to other support configurations.
In an article entitled "Problems of Patient Support: The Air Fluidised Bed as a Solution", pp. 269-275, Hargest discloses in FIGS. 1 and 2 conventional traction and equipment-supporting apparatus. Peck et al., in U.S. Pat. No. 3,063,066 entitled "Sidegate for Beds", discloses an extension rod mounted to a corner post cap for supporting equipment.
The use of telescoping posts or members in beds are well established. U.S. Pat. No. 3,081,463 issued to Williams et al. for "Motor Operated Hospital Bed" discloses telescoping corner posts supporting end panels. A cable system provides motorized activation. Similarly, U.S. Pat. No. 3,220,020 issued to Nelson for an "Adjustable Height Bed", discloses A bed with leg posts having a spring-biased telescoping outer sleeve that raises and lowers with the bed platform. Hillenbrand et al., in U.S. Pat. No. 3,237,212 entitled "Retractable Bed", also discloses a bed with leg posts having spring-biased telescoping outer sleeves that raise and lower the bed platform.
U.S. Pat. No. 3,742,527 was issued to Johnston et al. for a "Hospital Bed" having hydraulically driven telescoping corner legs and a guard rail with manually telescoping support legs. In U.S. Pat. No. 4,686,727 entitled "Convenience Bar Assembly for Hospital Bed", Wilkinson discloses a vertical bar and cross member for supporting various controls and patient equipment.
The equipment supports thus known in the art are either disposed on the bed in usable position, where they get in the way of the patient and nurses when not used, or they must be removed and stored, and thus may not be readily available when needed.
5. Weight-Sensing System
One of the advantages of the newer technologies has been the ability to monitor the patient while in the bed. An example of this is a system in which the weight of the patient is monitored while on the bed. The weight of the bed itself is compensated for in order to derive the patient's weight.
One such system is used in a bed made by Kinetic Concepts,Inc. of San Antonio, Tex. That bed has a display for showing the patient weight and change in weight.
The conventional structure providing this capability is the use of a stress gauge at each of four corners of the bed. Examples of this structure are disclosed in U.S. Pat. No. 4,669,136 issued to Waters et al. for "Combination Hospital Bed and Surgical Table" (col. 5, lines 13-25, col. 1, lines 58-60); and U.S. Pat. No. 4,926,951 issued to Carruth et al. for "Weigh Bed". This latter patent discloses a weigh system in which a load cell at each of four corners is supported on a base frame using a ball to transmit the vertical weight without creating any lateral torque. Horizontal position is maintained by three tie rods connecting the weigh frame to the base frame to prevent twisting of the weigh frame for certain patient or bed orientations.
One problem with such systems is that warp inevitable exists in either or both the bed frame or the base frame. This warping results in inconsistencies in the stress on the stress gauges, and therefor produces inherent inaccuracies or complexities that must be compensated for in some other way.
Not only is it useful to measure the weight of a patient without requiring the patient to leave the bed, it is also desirable to monitor the movement of a patient on the bed. Fleck et al., in U.S. Pat. No. 4,539,560 entitled "Bed Departure Detection System", discloses the use of tape switch detectors in a mattress to detect a person's departure from a bed. Restlessness of a person in the bed can be detected through the use of two or three tape switches.
Peck et al. devised a system for sensing the departure of a patient from the bed of the invention by a decrease in pressure in a lower bladder, as is disclosed in U.S. Pat. No. 4,803,744 entitled "Inflatable Bed".
6. Control Unit
As the complexity of beds and patient care systems increase, the complexity of control of the patient support system also increases. The control of some features, such as bed configuration, are made available to the patient, and control of other features, such as mattress pressure, air flow and temperature, are made available only to the attending personnel. Various control designs have been developed to accommodate these two control needs.
An air suspension bed identified by the proprietary name TheraPulse.TM. of Kinetic Concepts,Inc. of San Antonio, Tex., includes a hand-held bed controller provided with a hook for hanging the controller on a side rail. The bed also has controls extending from the face of the footboard for use by attendants. Pauna discloses a control panel mounted on a guard rail in U.S. Pat. No. 4,821,348 entitled "Convertible Bed and Bathroom Combination".
In U.S. Pat. No. 3,839,753 entitled "Hospital Bed", Benoit et al. disclose a nurse control panel located in the footboard and covered by a panel cover. These controls are in addition to patient controls. Drew et al. disclose various control units built into guard rails in U.S. Pat. No. 4,183,015 entitled "Side Guard for Bed Including Means for Controlling Remote Electrical Devices". This patent also mentions that removal, interchange, and replacement of the various controls is possible since the various controls are modular components. The controls may be easily replaced if service is required, or moved from one side to the other depending on the physical affliction of the patient. In patent '654, Vrzalik also discloses a control unit attached to the bottom of the footboard and control switches mounted in the footboard.
Except for the pendant control unit of Kinetics Concepts, such control units are mounted in fixed positions. The pendant control unit requires two hands to use, and is limited to controls made available to the patient. There thus remains the need for a controller that provides both attendant as well as patient controls that is variable in position and even capable of being hand held or removable in order to clear the patient area of the bed.
7. Transport Guide Wheels
One of the concerns with the newer, more elaborate beds is the strength and agility attendants need to maneuver them to different locations within a hospital. Typically, beds are provided with a wheel at each corner, with each wheel being free to turn about a vertical axis. This wheel arrangement is convenient for adjusting the orientation of a bed within a room, but makes turning corners and traveling along a straight line, such as when moving down a hallway, difficult.
Paramedic gurneys exist that have a fifth, center wheel that is fixed in alignment with the length of the gurney and is slightly below the plane of the four corner wheels. This assures that the fifth wheel is always in contact with the floor. However, the resulting rocking effect when weight is shifted from one end to the other is particularly undesirable in a permanent bed.
There is thus a need for a wheel system for hospital beds that allows maneuverability and yet assists in the movement of the bed significant distances.
8. Guard Rail Elevation System
As has been mentioned, beds typically have guard rails that can be fixed in a position above the mattress level, in order to keep patients from inadvertently exiting the bed. During times of attendance, it is desirable to remove the guard rail from its position. This is typically accommodated by making the guard rail removable or, more commonly, adjustable so that it can be pivoted or otherwise lowered below the level of the mattress.
One way that guard rails are lowered is by the use of telescoping support members, such as is described in U.S. Pat. No. 4,439,880 issued to Koncelik et al. for "Geriatric Bed Construction with Sideguards".
Cable and pulley systems are also used in various movable bed mechanisms in order to facilitate movement of a portion of the bed. For instance, Williams et al. disclose a cable-activated telescoping end panel in patent '463. Hunt et al., in patent '276, disclose the use of a cable and spring to operate a valve controlled by rotation of a pulley around which the cable is wound.
As is described in U.S. Pat. No. 4,747,171 entitled "Hospital Bed Rail Assembly", Einsele et al. developed a rail that pivots sideways to a lower position. It includes a spring, a cable and a cam link to resist gravity when lowered and raised.
There remains the need for a heavy duty side guard that raises and lowers in place, and is easy to operate with one hand.
9. Swing Arm Extension Brace
Hydraulic operation provides a readily controlled way to move articulating bed members. For example, Morrison developed a hydraulic ram for moving a pin resting on the edges of travel slots, as is shown in U.S. Pat. No. 3,462,772 entitled "Center-Pivoting Bed". This structure is confined to movement in the slots. Where a hydraulic arm is free to pivot it can experience a large bending moment when extended horizontally. It is therefore desirable to take advantage of the controllability of hydraulic arm movement while minimizing the size of the arm necessary to support a leveraged weight that can exist on the arm.
10. Platform Joint
Healthy people typically spend approximately one third of their time sleeping. People of what may be considered less than optimum health spend even greater amounts of time reclining. Beds of various forms have been developed in order to provide comfort to the user. This is particularly true of patients in hospitals and health care facilities, as well as those in homes who, for various reasons, are bed ridden.
Once one is in bed for extended periods of time in a situation or condition that does not allow movement in order to maintain comfort, complications, such as bed or pressure sores may develop. One way that this condition has been alleviated is to build beds having support surfaces that can be moved into various orientations and configurations. Representative examples of such beds are disclosed in U.S. Pat. Nos. 3,081,463 issued to Williams et al.; 4,038,709 issued to Kerwit; 4,099,276 issued to Hunt et al.; 4,371,996 issued to Nahum; 4,745,647 issued to Goodwin; 4,935,968 issued to Hunt et al.; and 5,023,967 issued to Ferrand; and French Pat. No. 87 16722 issued to Pupovic.
Each of these patents disclose beds having platforms formed of a set of panels that pivot for assuming configurations corresponding to various positions of a person's legs and torso. Each of these provide a back panel that supports a person's torso and a seat portion that supports the person's hips or hips and thighs.
These panels are typically hinged together or caused to pivot about a fixed joint corresponding to the hip joint. It has been observed that the surface length of the buttocks increases when a person moves from a flat reclining position to a sitting position. Fixed joints do not allow for this variation in body surface length, thereby requiring the reclining person to adjust her or his body to accommodate it. If the person is immobile, such accommodation is not possible. There therefore remains a need for a bed interpanel joint that is not fixed, but rather compensates for changes in the body surface during bending.
11. Hydraulic Valve
Many different forms of hydraulic valves exist for controlling fluid flow and fluid pressure. These valves typically involve a gate or plunger that closes an opening or other fluid passageway when in a closed position, and rapidly opens to relatively full flow conditions. There is thus very little intermediate control of the fluid flow.
In order to control fluid flow rate over a range of positions of adjustment, proportionally adjustable hydraulic valves have been developed. These valves provide for continuous variation of a fluid opening over a range of adjustment positions. Although the change in opening varies proportionally with adjustment position, the relationship between the two is very complex, with control determined typically by measurements of the fluid flow or the effect of the fluid flow, independent of adjustment position.
Articulating beds, and in particular hospital beds may use a hydraulic system to control movement of a support surface, such as a bed platform or hinging panels forming the platform, relative to a base supported on a floor. The platform may be moved as a unit, or the panels may move relative to each other. In such a bed, it is desirable to vary the speed of articulation of the support surface. For instance, it is desirable to raise the head panel slower than it is lowered. If the bed is capable of standing up a patient, it is desirable to use different stand up speeds for patients with different conditions.
It is useful to tilt a bed from side to side. For patients with pulmonary complications, tilting the bed from side to side slowly for long periods of time helps them breathe. However, if a bed needs to be tilted to position a patient for transfer to a stretcher, the bed must be tilted more quickly. Also for emergency applications, such as CPR or Trendelenburg, it is desirable to get the bed in a particular configuration very quickly. Since the bed could be in any allowable configuration at the time of the emergency request, the cylinders must all move at one speed for normal use, and another speed for emergency use.
It is seen that speed control over a wide range is desirable. Conventional valves typically of the spool type and have a wide dynamic range of operation. The portion of the range applicable to articulation speeds for beds is a small portion of that range. These valves also have flow rates that vary relative to valve shaft position according to complex equations. As a result they are themselves expensive and also require expensive systems to control them.
There thus is a need for an hydraulic articulating system that provides control within a limited range that is economical, and is controllable simply.
12. Platform Support
Various apparatus have been developed for supporting a bed platform. Current designs provide for changing the elevation and attitude of the platform relative to the base frame. Conventional systems use linear drives on parallel linkages or one or more hydraulic cylinders positioned to change the pitch and roll of the bed relative to a central universal joint.
A simplified platform support system was developed by Ferrand, as disclosed in U.S. Pat. No. 5,023,967, that involves a triangulation support system providing full platform articulation using three platform supports. The patent discloses the use of a universal joint mounted to the platform and supported on two opposing hydraulic arms. A pair of laterally opposing side arms are spaced from the universal joint. Coordinated adjustment in the lengths of the various hydraulic arms adjusts the three basic forms of platform orientation: pitch, roll and elevation.
Although providing a simple and effective system for articulating a platform, the three-axis support system as disclosed by Ferrand requires the use of two heavy-duty base hydraulic rams for supporting the universal joint. A compact universal joint, as disclosed, results in a mechanically weak point when the forces of an articulating bed platform are applied to it. By attaching the upper ends of both base rams to the universal joint, the available range of motion of the platform is equal to the adjustable length of the rams. Further, by mounting the two side arms to the base frame or to the base of the adjacent base ram, elevation changes in the bed are further limited by the length of throw of the two side arms. The attachment of the universal joint and the side legs to different, relatively hingeable panels also requires the use of a control system that must account for changes in orientation between the associated panels. There thus is a need for a three-axis support system that is more economical to produce and easier to use.
13. Multifunction Control System
As beds become more sophisticated with an increasing variety of different features, the use of the various features becomes more complicated and it becomes increasingly difficult to coordinate the various features and keep track of the state each feature is in at a given time. Such coordination becomes increasingly important when the bed is used to support a patient in a critical condition.
Beds presently exist which allow an attendant to lockout the control of bed movement by the patient in order to assure that the bed is maintained in a selected support configuration. An example is where the patient is held in traction and the orientation and firmness of the mattress must stay the same. Also, if the bed has an equipment-support table that extends over the mattress, certain movements of the mattress could upset the table. As yet another example, it would be unsafe to tilt the mattress sideways if one or more of the "downhill" guardrails is not in an upright position. There is therefore a need for a bed having controls that assist in the coordination of various features of the bed to assure proper patient treatment and safety.